The low penetration depth of optical waves (generally about 200 nm to about 2 μm) in tissue (i.e. generally about 2 mm to about 3 mm) limits the clinical application of optical imaging instrumentations, such as optical coherence tomography (OCT), and the like. Therefore, hand-held or endoscopic probes are highly desired for clinical and therapeutic applications, however such probes tend to suffer from various problems.
OCT probes, and the like, can be divided into two categories based on their scan modes: side imaging and forward imaging. Side-imaging probes are the most widely used since they tend to have a much simpler actuation mechanism than forward-imaging probes, and the actuation mechanism tends to be far away from the probe tips. Further, side-imaging probes tend to be very flexible and have small size. However, such side-imaging scanning probes only provide side imaging around the probe which limits its clinical applications, such as image-based surgical needle guidance. Thus, forward-imaging probes, whose size tends to be in a range of needle size, can be more suitable for surgical guidance for brain, retinal and ovarian surgery.
However, forward-imaging probes are generally more complicated in design and require the actuator near the probe tips. Currently the size of the forward-imaging OCT probe is mainly limited by the size of the actuation mechanism. For example, forward-imaging probes using MEMS (micro-electromechanical system) mirrors generally have a diameter in a range of about 3 mm to about 6 mm due to the electronic control cable used with forward-imaging probe. Further, forward-imaging probe are generally housed in a thin-wall hypodermic tube using a PZT actuator with an overall diameter of about 2.4 mm.